Correct several behavior descriptions in comments.

Reuse cautionary language from src/test/ssl/README in
src/test/kerberos/README.  SLRUs have had access to six-character
segments names since commit 73c986adde5d73a5e2555da9b5c8facedb146dcd,
and recovery stopped calling HeapTupleHeaderAdvanceLatestRemovedXid() in
commit 558a9165e081d1936573e5a7d576f5febd7fb55a.  The other corrections
are more self-evident.

1 files changed, 5 insertions, 5 deletions

diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c
index 5189a5ad5e3..23eb605d4cb 100644
--- a/src/backend/commands/vacuum.c
+++ b/src/backend/commands/vacuum.c
@@ -949,11 +949,11 @@ vacuum_set_xid_limits(Relation rel,
 	/*
 	 * We can always ignore processes running lazy vacuum.  This is because we
 	 * use these values only for deciding which tuples we must keep in the
-	 * tables.  Since lazy vacuum doesn't write its XID anywhere, it's safe to
-	 * ignore it.  In theory it could be problematic to ignore lazy vacuums in
-	 * a full vacuum, but keep in mind that only one vacuum process can be
-	 * working on a particular table at any time, and that each vacuum is
-	 * always an independent transaction.
+	 * tables.  Since lazy vacuum doesn't write its XID anywhere (usually no
+	 * XID assigned), it's safe to ignore it.  In theory it could be
+	 * problematic to ignore lazy vacuums in a full vacuum, but keep in mind
+	 * that only one vacuum process can be working on a particular table at
+	 * any time, and that each vacuum is always an independent transaction.
 	 */
 	*oldestXmin = GetOldestNonRemovableTransactionId(rel);